[R] registration of C routines

[Setzer.Woodrow@epamail.epa.gov]

Thanks; I now have the documents you mentioned.

I knew about R_FindSymbol, but I guess I was hoping to find it was really
stable enough to be part of the API, even though it is not listed there.  I
was hoping to use it to extend my ODE package odesolve (on CRAN), to be
able to directly handle systems of odes written directly in C or Fortran,
and bypassing the R call-back mechanism.  Odesolve uses callbacks into R,
so that I use compiled Fortran code to solve a system of odes written in R.
The idea was that, in R, I would dyn.load a shared library that contained
the ode function, then call "lsoda()" (from odesolve), passing a string
that gives the name of the function to be integrated.  The string would be
passed to the C wrapper I have around the actual ode solver, where
R_FindSymbol would return a function pointer.

R. Woodrow Setzer, Jr.                                            Phone:
(919) 541-0128
Experimental Toxicology Division                       Fax:  (919) 541-5394
Pharmacokinetics Branch
NHEERL MD-74; US EPA; RTP, NC 27711


                                                                                                                      
                    Duncan Temple Lang                                                                                
                    <duncan at research.bell        To:     Woodrow Setzer/RTP/USEPA/US at EPA                              
                    -labs.com>                   cc:     r-help at hypatia.math.ethz.ch                                  
                                                 Subject:     Re: [R] registration of C routines                      
                    07/19/01 10:07 AM                                                                                 
                                                                                                                      
                                                                                                                      





Hi,,

  There are 3 different places you can find out more about the
registration mechanism. The place to find code examples
is in the libraries in the R distribution. For example, take a
look at
  src/library/ctest/src/init.c

Also, I have collected the descriptions (drafts) I have written
about this. They are available from
  http://cm.bell-labs.com/stat/duncan/R


The C routine R_FindSymbol() is the internal mechanism that finds a
native symbol by name in a package. It is not in the official API, so
is subject to change. Hence it is not a good idea to write your code
to depend on it, but your mileage may vary depending on the context,
etc.

Personally, I would think that it might be better to avoid this
low-level dependency. You might be better off linking the DLL/.so from
the secondary package with that in the first package.  Alternatively,
on some platforms, you can specify the value of the local argument as
FALSE for dyn.load() and library.dynam() and that makes the symbols in
that library visible to all the others. Then your C code can call the
routine directly. This has potential danger based on how dlopen()
works on each system and the order in which the libraries have been
loaded.


  D.


Setzer.Woodrow at epamail.epa.gov wrote:
> Almost at the end of the News for R-1.3.0 is the following section:
>
> o   New mechanism for explicitly registering native routines in a
>      DLL/shared library accessible via .C(), .Call(), .Fortran() and
>      .External().  This is potentially more robust than the existing
>      dynamic lookup, since it checks the number of arguments, type of
>      the routine.
>
> How do I learn how to use this mechanism?  Also, is there a sanctioned
way
> to find and use, in C-code loaded via dyn.load and executed using one of
> the calls .C(), etc., functions defined in a separate DLL/shared library
> and also loaded with dyn.load?
>
> R. Woodrow Setzer, Jr.                                            Phone:
> (919) 541-0128
> Experimental Toxicology Division                       Fax:  (919)
541-5394
> Pharmacokinetics Branch
> NHEERL MD-74; US EPA; RTP, NC 27711
>
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--
_______________________________________________________________

Duncan Temple Lang                duncan at research.bell-labs.com
Bell Labs, Lucent Technologies    office: (908)582-3217
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